Abstract. Within the last years pollen grains have gained increasing attention due to their cloud forming potential. Especially the discovery that ice nucleating macromolecules (INM) or subpollen particles (SPP) obtained from pollen grains are able to initiate freezing has stirred up interest in pollen. INM or SPP are much smaller and potentially more numerous than pollen grains and could significantly affect cloud formation in the atmosphere. However, INM and SPP are not clearly distinguished and explanations on how these materials could distribute in the atmosphere are missing. In this study we focus on birch pollen and investigate the relationship between pollen grains, INM and SPP. According to the usage of the term SPP in the medical fields we define SPP as the starch granules contained in pollen grains. We develop an extraction method to generate large quantities of SPP and show that INM are loosley attached to SPP. Further, we find that purified SPP are not ice nucleation active: after several times of washing SPP with ultrapure water the ice nucleation activity completely disappears. To our knowledge this is the first study to investigate the ice nucleation activity of isolated SPP. To study the chemical nature of the INM we use fluorescence spectroscopy. Fluorescence excitation-emission maps indicate a strong signal in the protein range (maximum around λ_ex = 280 nm and λ_em = 330 nm) that correlates with the ice nucleation activity. In contrast, with purified SPP this signal is lost. We also quantify the protein concentration with the Bradford assay. The protein concentration ranges from 77.4 μg mL⁻¹ (Highly concentrated INM) to below 2.5 μg mL⁻¹ (purified SPP). The results indicate a linkage between ice nucleation activity and protein concentration. Even though purified SPP are not ice nucleation active they could act as carriers of INM and distribute those in the atmosphere.

中文翻译：

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桦树亚花粉颗粒（SPP）作为冰核大分子的载体

摘要。在过去的几年中，花粉粒由于其形成云的潜力而受到越来越多的关注。特别是从花粉粒获得的冰核大分子（INM）或亚花粉颗粒（SPP）能够引发冻结的发现激起了人们对花粉的兴趣。INM或SPP比花粉小得多，并且可能比花粉小得多，并且可能显着影响大气中的云形成。但是，INM和SPP不能清楚地区分开，也缺少有关这些物质如何在大气中分布的解释。在这项研究中，我们重点研究桦树花粉，并研究花粉粒，INM和SPP之间的关系。根据医学领域中术语SPP的用法，我们将SPP定义为花粉粒中所含的淀粉颗粒。我们开发了一种提取方法来生成大量的SPP，并表明INM松散地附着在SPP上。此外，我们发现纯化的SPP没有冰核活性：在用超纯水洗涤SPP几次后，冰核活性完全消失。据我们所知，这是第一个研究分离的SPP的冰核活性的研究。为了研究INM的化学性质，我们使用荧光光谱法。荧光激发-发射图表明在蛋白质范围内有一个强信号（最大在λ附近 据我们所知，这是第一个研究分离的SPP的冰核活性的研究。为了研究INM的化学性质，我们使用荧光光谱法。荧光激发-发射图表明在蛋白质范围内有一个强信号（最大在λ附近 据我们所知，这是第一个研究分离的SPP的冰核活性的研究。为了研究INM的化学性质，我们使用荧光光谱法。荧光激发-发射图表明在蛋白质范围内有一个强信号（最大在λ附近_ex  = 280 nm，_λem  = 330 nm）与冰的成核活性相关。相反，使用纯化的SPP会丢失此信号。我们还使用Bradford分析定量蛋白质的浓度。蛋白质浓度范围从77.4μgmL ^-1（高度浓缩的INM）到2.5μgmL ^-1以下（纯化的SPP）。结果表明冰成核活性和蛋白质浓度之间的联系。即使纯化的SPP没有冰核活性，它们也可以充当INM的载体并将其分布在大气中。